Eggs typified by chicken eggs and the like include eggs for hatching chicks, in addition to table eggs. Such eggs are particularly referred to as “hatching eggs”. When a hatching egg is incubated for prescribed days under certain environment such as a prescribed temperature, a chick hatches. In a hatchery where a large number of chicks are hatched, the production process is managed such that hatching eggs obtained within a certain period can hatch all together on the same prescribed day.
Inside a hatching egg, development of an embryo progresses from the point of egg laying. Therefore, first, in the step of accumulating hatching eggs obtained within a certain period, the hatching eggs are kept under the environment in which the temperature is equal to or lower than 28° C., to suppress the embryonic cell division and cause the hatching eggs to diapause. When the prescribed number of hatching eggs are accumulated, preliminary heating is performed to resume the activity of the resting embryos. The hatching eggs are inspected for grime or cracks, and are placed on a dedicated tray referred to as “setter tray”. The hatching eggs housed in the setter tray are kept under the environment in which the temperature is 38° C., and thereby, the hatching eggs enter the incubation process. A date of starting the incubation process is defined as an incubation starting date, and the number of days elapsed from the incubation starting date is defined as the number of incubation days. The chicks are born almost on day 21 of the number of incubation days.
On day 18 or 19 of the number of incubation days, the work of moving the hatching eggs from the setter tray to a dedicated tray referred to as “hatcher tray” is performed in preparation for incubation of the hatching eggs. When this work of moving is performed, a prescribed inspection is performed on the hatching eggs. The inspection will now be described.
Even for the hatching eggs, not all of the hatching eggs hatch, and the hatching eggs may include some unfertilized eggs at a certain rate from the beginning, or may include some growth-stopping eggs in which the growth of an embryo stops during the course of the incubation process. Some of these unfertilized eggs or growth-stopping eggs go rotten at the contents and the contents-rotten egg is called “spoiled egg”. The rotten contents generate gas. When the gas is generated in a space closed by a shell, the pressure inside the egg becomes high, and thus, some of the spoiled eggs burst. The inventors describe such burst egg or an egg that may burst as “explosion egg”.
When a hatching egg housed in the setter tray explodes (bursts), the rotten contents are scattered and miscellaneous bacteria included in the contents contaminate even the surrounding healthy hatching eggs. When the hatching egg explodes after movement to the hatcher tray, the already born chicks may be contaminated.
Even in the case of the spoiled egg that does not explode, the contaminated contents inside the egg may seep out to the surface of the egg due to the pressure of the gas generated in the egg. In this case as well, it is conceivable that transfer of the contents that have seeped out to the surface of the egg results in contamination of the surrounding healthy hatching eggs and the tray. Furthermore, when the hatching egg is vaccinated, the hatching egg having the increased inner pressure may explode due to the impact when an injection needle comes into contact with the shell.
In order to prevent such contamination, inspection is performed to divide the hatching eggs into healthily grown hatching eggs and unfertilized eggs, growth-stopping eggs or the like. Namely, the viability of the hatching eggs is determined. As proposed in, for example, PTD 1 (Japanese Patent Laying-Open No. 09-127096) or PTD 2 (WO 2009/044243), an optical method has been conventionally used to determine the viability of hatching eggs. According to this method, the viability is determined by emitting the prescribed light toward a hatching egg and analyzing a time-varying component of the light that has transmitted through the hatching egg. A hatching egg determined to be an unfertilized egg or a growth-stopping egg in this manner is removed immediately, which prevents the healthily grown hatching eggs from being contaminated.